This invention relates to photographic developing apparatus and particularly to apparatus for rocking photographic developing trays.
Processing of black and white photographic prints requires three solutions: developer, stop bath, and hypo or fixer. The typical amateur or professional photographer who processes his own prints uses three rectangular flat bottom developing trays placed in a row in a darkroom sink, with a different one of the solutions in each tray. After exposure, the prints are placed in the developer solution first and the tray agitated so that the developer flows back and forth from one end of the tray to the other, thereby continually washing fresh solution over the prints. After a developing period of approximately 2 minutes, the prints are transferred to the tray containing the stop bath and agitated for about 20 seconds to stop further development of the print. The prints are then placed in the last tray of hypo, and this tray is agitated for approximately 6-10 minutes to fix the print.
There are four standard sizes of photographic developing trays corresponding to print sizes of 5 by 7 inches, 8 by 10 inches, 11 by 14 inches and 16 by 20 inches, the actual dimensions of each tray being about two inches larger than the nominal dimensions. The choice between sizes will be dictated by the number and dimensions of the prints to be processed.
Commonly the tray agitation is done by hand, but this becomes tiresome, particularly during the fixing cycle. In addition, it is difficult to agitate the trays while simultaneously checking the progress of the development and moving the prints from one bath to the next.
Various devices have been suggested for automating the tray rocking process. One such device, shown in U.S. Pat. No. 3,478,666 to L. H. Bishop, includes a tray platform supported on a housing for four-way rocking motion about intersecting axes lying in a common plane. The four-way rocking motion is achieved by a motor-driven arm mounted in the housing underneath the platform. The arm rotates about a vertical axis and carries a drive bearing at its outer end for engaging four cams attached to the underside of the platform at angular spacings of 90.degree.. A similar tray rocking apparatus, in U.S. Pat. No. 2,494,866 to A. J. Fressola, comprises a tray platform oscillated about fixed horizontal intersecting axes by means of a pair of cams mounted on right-angled shafts coupled by a pair of bevel gears and driven by a single motor.
In still another known arrangement, a rectangular tray platform is positioned by means of spaced parallel ribs extending from its underside, for pivoting motion about its longitudinal axis on the edge of a long metal strip set upright in a heavy wooden base. An electric motor drive is connected through a crank arrangement to one side of the platform for oscillating it on the knife-edge support strip.
The above platform-type of tray rockers hold only one tray, or two at the most; so that it is necessary either to shift trays on and off the platform or to purchase two or more rocking machines because a platform large enough to accommodate three of the largest size trays would be impractically large, heavy, and expensive.
Shifting single trays of successive processing solutions off and on a small rocker platform not only is a tedious chore that tends to cause spills and mess but also may result in spoiled prints because of delays in moving the prints from one bath to the next. Furthermore, it is desirable to rock all three trays continuously so that prints can be processed at a steady rate rather than in batches of a few at a time through the entire process.